Expandable mandrels have been used for applications where parts must be quickly mounted onto and subsequently removed from a mandrel, the part having a generally cylindrical mounting hole for mounting to a shaft for rotating the part. Two classic applications are part inspection, where the part is mounted to the mandrel to allow measurement of its concentricity or other dimensions, and part fabrication, where a blank is mounted to the mandrel to allow it to be machined to fabricate the part such as by grinding, turning, and/or other manufacturing operations. In either case, there is a need for the part to be quickly mounted so as to be concentric with the mandrel.
Over the years, several expandable designs for mandrels have been employed. Classically, such expandable mandrels employ a shank having longitudinal slots that are slidably engaged by a number of keys. The slots are sloped relative to a longitudinal axis of the shank, and the keys have bottom surfaces which are similarly sloped such that, as the keys slide in the slots, their separation from the shank axis either increases or decreases. A sleeve movably engages the shank and the keys and serves to force the keys to slide along their respective slots in a coordinated manner. When a part is to be mounted to the mandrel, the mounting hole of the part is placed about a portion of the keys and the sleeve is moved to force the keys outwards to grip the part. One early patent, U.S. Pat. No. 198,633, teaches a sleeve which slidably engages the shank, allowing more rapid mounting and dismounting of parts than is possible with earlier expanding mandrels, where the sleeve is threadably engaged with the shank. Sliding sleeves are employed in most modern expanding mandrels.
While employing the same basic scheme for securing a part to the shank, expanding mandrels differ in details of their structure. The shanks have distal ends that may be either cylindrical or frusto-conical, in the latter case tapering as the distal end is approached. Similarly, the designs may differ in the configuration of tension springs employed to maintain the keys slidably engaged in their respective slots and in the structure for engaging the sleeve with the keys so as to coordinate the longitudinal motion of the keys.
U.S. Pat. No. 2,544,633 teaches a mandrel that employs a sleeve having radially-extending passages that slidably engage protrusions on each of the keys to control the longitudinal position of the keys. The mandrel of this patent also employs a tension spring that surrounds the keys to hold them in their slots, the tension spring engaging the keys at a location between the sleeve and the distal end of the shank.
While existing expanding mandrels allow parts to be mounted and removed readily while providing accurate concentricity with the mandrel shank, in all the above designs the part may vary in its axial position when mounted. This variation in the axial position frequently requires an operator to adjust the axial position of the mandrel to assure that the part is in a desired location for inspection or machining. To avoid this additional step, there is a need for an expandable mandrel which can quickly secure a part at a desired axial location along the length of the mandrel.